Competition. Mutually negative interaction between two species in the same guild or trophic level Changes in abundance, fitness, or some fitness component (growth, feeding rate, body size, survival). Topics for today. Mechanisms and models of competition Evidence for competition
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Values of population sizes of two species, N1 and N2, that result in positive, negative, or zero population growth for interacting species. The zero growth isoclines are shown as a solid line for species 1 and a dashed line for species 2. [from Morin 1999]
K is carrying capacity; dN/dt is population growth rate; a is competition coefficient with a12 being effect of sp. 2 on sp.1
Figures from Gotelli, “A Primer of Ecology”
...of species 2 by species 1
...of species 1 by species 2
Figs from Gotelli
“winner” depends on priority effects
Figs from Gotelli
Poor competitors remove less N
Good competitors remove more N
Roots are the foraging organ: mass correlated with N assimilation
Tilman and Wedin 1991
Wedin and Tilman 1993.
Nucella = Thais lapillus
Similar body size and perch height
Little overlap in size or perch height
Pacala and Roughgarden 1982
High body size and perch height overlap
results in competition
Strong et al 1979
Large-beaked G. fortis (A) and G. magnirostris (B) can crack or tear the woody tissues of T. cistoidesmericarps (D), whereas small-beaked G. fortis (C) cannot.
Drought causes competition: selects for divergent (small) beaks in fortis
magnirostris introduced: has really large beak
Grant and Grant 2006
Canine size for each species/sex in two locations
Dayan et al 1990
Muchhala and Potts 2007
“As species of the same genus have usually, though by no means invariably, some similarity in habits and constitution, and always in structure, the struggle will generally be more severe between species of the same genus, when they come into competition with each other, than between species of distinct genera.”
If habitats select for particular traits, and related species share traits, expect phylogenetic clustering (“habitat filtering”)
If competition or other density-dependent factors are stronger between relatives than between distant relatives, expect phylogeneticoverdispersion
Webb 2000: evidence for habitat filtering in tropical trees
NRI: species more related than expected (clustering); NTI: not different from random (do NOT see overdispersion)
Cavender-Bares et al 2004: evidence for competitive exclusion in oaks
Using experimental estimates of competition, closely related species do not compete more intensely
Cahill et al 2008
These are correlations between competitive effect and phylogenetic distance.
What do you expect this correlation to be if closely related things compete more intensely?
Fargione et al 2006
Net effect: Difference between total biomass in a plot and average biomass of monocultures increases over time
Complementarity: when positive (as here) means species have higher than expected yield in mixture (attributed to N-fixers and C4 species presence in high-diversity mixtures)
Selection: if positive would mean that species with high monoculture biomass are competitive dominants, and when present (by chance) create more total biomass in diverse plots
Fargione et al 2006
Cadotte et al 2009
Booth, R. E., and J. P. Grime. 2003. Effects of genetic impoverishment on plant community diversity. Journal of Ecology 91:721–730.